Synchronizing mechanism



y 1954 E. w. PAPPENFUS ETAL 2,678,966

SYNCHRONIZING MECHANISM Filed Feb. 4, 1952 INVENTOR. g y 1 1700501 1. 841610 4;- ronbvtr Patented May 18, 1954 OFFlCE SYN CHRONIZIN G MECHANISM Ernest W. Pappenfus and Robert L. Craiglow, Cedar Rapids, Iowa, assignors to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application February 4, 1952, Serial No. 269,732

6 Claims. 1

This invention relates in general to a synchronizing circuit, an in particular, to a coarse and fine phase and frequency synchronizing systern, for the receiving terminal of an automatic code communication system.

Automatic code communication systems, such as teletypes, have a specific code group for each letter of the alphabet or for each symbol to be transmitted. The code group consists of a current or voltage varying in time in a specific manner relating to the particular symbol being transmitted. In order to be able to separate the individual code groups from one another, it has become customary to precede each code group with a start pulse and to succeed each code group with a stop pulse. The start and stop pulses are, in general, of different character, such as currents of opposite polarity. Such automatic code communication systems utilize flying brushes at the transmitting terminal to initiate the start and stop pulses and at the receiving terminal to separate the start and stop pulses from the code group. In order for the flying brush at the receiving terminal to separate the start and stop pulses from the code group and to separate the code element from the code group, it must run in very close synchronization with the flying brush at the transmitting terminal. Such systems are well known to those skilled in the art and for a more detailed description, reference may be made to pages 109 through 118 of Principles of Electricity Applied to Telephone and Telegraph Work, 1938 edition, American Telephone and Telegraph Company.

It is an object of this invention, therefore, to

provide an automatic synchronization system which will synchronize the receiving terminal flying brush with the transmitting terminal flying brush and, after a sufficient synchronizing time, to provide an artificial start and stop pulse in those cases where those transmitted were altered by some type of interference such as noise.

Further objects, features and advantages of this invention will become apparent from the following description and the claims when read in view of the drawing, in which;

The figure is a schematic view of this invention.

For explanation purposes, let it be assumed that the start and stop pulses, whatever their original voltage or current, are converted to negative and positive pulses respectively; these pulses being of equal magnitude and of opposite polarity.

The figure illustrates a pair of terminals in flying brush 3!}! of the flne synchronization detector, and to flying brush tut of the coarse synchronization detector. Input signal terminal H is connected to ground. The received code signals, after having been converted so that the stop and start pulses are of equal magnitude but of opposite polarity with the start pulse negative, are connected to terminals [0 and H.

The synthetic start-stop pulse generator 200 The signal input terminal ii] is connected to the code wheel segment 2&2. Segment 2% is connected to the positive terminal of battery 205 and segment 2% is connected to the negative ter minal of battery 2%. The other terminal of batteries 205 and 2% are connected to ground. The flying brush 2!]! is driven by a shaft 555? and is connected to terminal l3 of the signal out put terminals.

After synchronism has been obtained between the transmitting and receiving flying brushes as will be described latter, the flying brush 2M will be in contact with segment 254 when the start pulse is being transmitted. Likewise the flying brush 2%! will be in contact with segment 283 when the stop pulse is being transmitted. During the remainder of the time the flying brush 2M will be in contact with segment 2G2 and connects the input terminal it to the output terminal it, thus transferring the input signal code group directly to the output terminal. When the flying brush 2st is on segment 2H3, a synthetic stop pulse is generated by battery 295 and applied to terminal it. When the flying brush it: is on segment its a synthetic start pulse is generated by battery 2% and applied to terminal it. Thus at the output terminals l2 and [3 the original code group applied to terminals to and II are obtained plus a synthetic start and stop pulse. Should interference cause the start or stop pulse to be modifled, the synthetic start and stop pulse generator will supply these pulses at the correct time.

The signal output terminal I2 is connected to ground. Terminals I 2 and I3 would normally 3 be connected to a decoding device such as a teletypewriter.

Fine synchronizing detector 300 The flying brush Sill is driven by shait bill and is connected to input terminal it. The short segment 392 is connected through resistor not to the grid of tube V-l. Resistor 3G4 and capacitor M35 are connected from grid to cathode of tube V-l. to ground. and the plate is connected through half a polar relay winding tilt to the positive terminal of battery 3st. The negative termi nal of this battery is connected to ground. The cathode of a balancing tube V4 is connected to ground while the grid is connected to cathode through resistor 301.

The plate of tube V-2 is connected through half the polar relay winding 30% to the positive terminal of battery 3%. When the currents through the two halves of the polar relay winding 308 are equal, the armature etc will midway between the two contacts. An unbalance of current through the two halves of the polar relay winding see will. cause the armature to make contact with 3M] or 3H depending on the direction of the unbalance. Armature 3529 is connected through armature til and contact Mil to the common terminal oi shaded pole windings 5133, 5%, 6st and 584. Contact 3553 is connected to one end of windings and cs3 and contact 3H is connected to one end of windings 58 i and EM.

After approximate synchronisin has been oo-- tained between flying brush is: and the mitter flying brush, flying brush Bill will be in contact with segment 392 during the transition between the stop and start pulses of the incoming signal. Under conditions of perfect synchronism the segment 3&2 will be subjected to plus and minus voltages for equal lengths oi time and after brush 3M has broken contact with segment 392, there will be no residual charge left on capacitor 395 and thus, the grid poten tial on tube V--! will be zero. Since the potential on the grid of tube V-Z is also zero, the armature 309 will rest between the two contacts 3m and 3| I. Should the synchronization be such that the negative start pulse or the positive stop pulse persist longer on segment tilt, capacitor sss would be left with a negative or positive residual charge, respectively. This would cause an unbalance in the current drawn by tubes V4 and V-2 and, therefore, deflect the armature 399 to contact 31s or 3. This will cause motor armatures 5M and 6st to run in such a direction as to correct the synchronization error as will be described later.

Coarse synchronising detector 400 Flying brush Mil is driven by shaft 5st and is connected to the signal input terminal it. Segment M12 is connected through battery silt to the grid of tube V-3. Capacitor 41c connects the grid of tube V-t to ground. The cathode of tube V-t is connected to ground while the plate is connected through one half of a neutral relay winding M3 to the positive terminal of .a battery M2.

Segment M3 is similarly connected to tube V- l except that the positive terminal of battery M34 is connected to segment 4502 while the negative terminal of battery 495 is connected to segment e93. Relay armatures 4M and iii are shown-in the non-energized position. Should any unbalance of the currents in tubes V4 and V 3 exist The cathode of tube V-i connected iii . 553d, 5523 and SM.

regardless of the direction or unbalance, armature 4H1 will break contact with lit and make contact with M5, while armature M1 will break contact with 418.

When approximate synchronization has been obtained, the negative start pulse will be re ceived during the entire time that flying brush as! is in contact with segment edit. Since battery 465 is equal and opposite to the start pulse potential, no current will charge capacitor H5 and the residual charge on this capacitor will be zero. Similar reasoning will show that when the positive stop pulse is received during the entire time that flying brush 4m is in contact with segrnent 462, the residual charge on capacitor tit will be zero.

Since, under the aforementioned conditions, the potentials on the grid of tubes we and V- l are zero, the current through the two tubes will equal and the relay winding 1313 will not be energized and alternating current will be supplied to the field winding through armature lit and contact H6. Also relay armature All will be in contact with thus connecting armature 369 to one side of the motors shaded pole windings 5513, EM, and set, and the fine synchronising detector will control the rotation of motor armature 5m and 581.

Should a gross error in synchronism occur so that a positive voltage is not received during the entire time the flying brush tell is in contact with segment it}. and/or a negative voltage is not received during the entire time the flying brush at! is in contact with segment 5&3, relay winding M3 will be energized due to an unbalance of the currents in tubes V-El and VA. This will break the contact between armature All and contact Ms, thus disabling the control of armature sec on the shaded pole windings 5213,

Also armature are will disengage with contact 4n; and engage contact are thus tie-energizing fleld and energizing the timer motor field ii.

Frequency corrector 600 The frequency corrector consists of a frequency standard 685 that be a crystal, whose output drives a synchronous motor set. The shaft sec of this motor drives a difierentialgear 59%. The frequency of the frequency standard can be varied slightly by rotating shaft 6515 which might be connected to trimmer capacitor that would produce this change. Shaft tilt is driven by motor armature bill with its associated field winding tilt: and shaded pole windings i353 and 604. When the flne synchronizing detector is in operation the field winding is energized from the alternating current source It and the direction of rotation of armature tfil will dependon which of the two shaded pole windings is shorted by armature Silt. If neither is shorted, the armature iiill will be stationary. Thus, any. difference the frequency of the transmittcrand receiver rlyingbrush will eventually result in a phase error of sufflcient magnitude to cause the fine synchronizing detector to operate motor armature Elli in the direction necessary to correct this frequency error.

Alternating current power source. 14

The alternating current power source it would normally be supplied from a 110 Volt 5!) cycle power line. It is represented, here in the interest of completeness as a generator, This power sourcesupplies the timing motor It, the

phase corrector motor M and the frequency corrector motor BOI.

Timer motor 16 The timer motor winding if is energized. by relay armature 4M when a gross error in synchronization is apparent. This motor moves contact arm l8 toward contact [9. After a specified interval of time has elapsed, arm is will contact 19 thus shorting shaded pole winding 594 and causing motor armature 501 to increase the speed of shaft 501 by means of the differential gear 506. Because the shaft is now operating well above synchronous speed, the receiving flying brushes will eventually reach phase synchronism with the transmitter flying brush which will immediately cause the course synchronizing detector to de-energize winding l1 and open contacts l8 and I9. At this time the fine synchronizing detector will resume control.

Phase corrector 500 of the differential gear 506. Thus, the angular velocity of shaft 501 can be either accelerated or retarded with respect to shaft 668. This provides a fast means of correcting any phase error between the transmitting and receiving flying brushes While the frequency of the frequency standard 606 is being synchronized with the transmitting terminal equipment.

Rsum

To illustrate more clearly the functions performed by this device, let us assume that a radio teletype communication system provides a polar teletype signal at the receiving terminal equip ment which is connected to the signal input terminals l0 and II and that the output terminals I2 and I3 are connected to a teletypewriter. In estaplishing the initial synchronization, contact arm l8 would be manually closed. This would cause the flying brushes at the receiving terminal to rotate faster than those at the transmitting terminal until the brushes at the receiving terminal came into phase coincidence with the transmitting brush. At this time the coarse synchronizing detector 400 would cause the fine synchronizing detector 300 to take control of the phase and frequency corrector motors and thus maintain synchronization.

After synchronization has been obtained the start and stop pulses would be supplied to the teletypewriter even in the presence of severe noise. This would insure that the proper number of letters would be printed even though noise might cause them to be printed incorrectly. However, the readability would be improved and incorrect letters could be interpolated from the context of the message. Also, without this system, several letters may be missed due to a single noise pulse since it disturbs the synchronization of the teletypewriter. The effect of isolated noise pulses on the synchronizing circuits can be minimized by making the charging time of capacitor 305 very long and also by using a slow acting relay M3. Complete fading for short periods of time will not cause loss in synchronization since the fine synchronizing detector is disabled and the timing motor contacts will not have closed. Complete fading for long periods of time will automatically reinitiate the process described under initial synchronization.

Although this invention has been described with respect to a particular embodiment thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention as defined by the appended claims.

We claim:

1. A synchronizing mechanism for a teletype receiver comprising, a pair of input terminals receiving the input signal thereon, a synthetic start-stop pulse generator having a code wheel, a first flying brush, three segments mounted about said code wheel with two of said segments being of the same size and both substantially smaller than the three, said first flying brush engageable with said three segments, a first battery connected between one of the input terminals and one of the smaller segments with the positive terminal of the battery connected to the segment, a second battery with the same potential as the first battery connected between the second segment and the same input terminal with the negative terminal of the battery connected to the segment, a pair of output terminals one of which is connected to one of the input terminals and the other connected to the first flying brush, a fine synchronizing detector comprising a fourth segment, a second flying brush, a pair of resistors connected in series between the fourth segment and ground, a condenser in parallel with the grounded resistor, a first balancing tube with its control grid connected to one side of said condenser, a second balancing tube connected in a balanced circuit with said first balancing tube, a polar relay with its actuating winding connected between the first and second balancing tubes, a switch controlled by said polar relay and movable between a pair of contacts, a driving means connected to said first and second flying brushes, a pair of corrector s; motors connected to said switch, one of said corrector motors connected to add its shaft output to the drive shaft of said driving means, a frequency standard supplying an input to said driving means and the other corrector motor connected to control the output frequency of the frequency standard.

2. Means for synchronizing a receiving terminal with a transmitting terminal comprising, three flying brushes, a drive shaft connected to said three brushes, a differential gear connected to the drive shaft, a drive motor supplying an input to said differential, a frequency standard supplying an input to said drive motor to control its rate of rotation, three segments mounted about the first flying brush and engageable therewith with the first two of said segments substantially smaller than the third segment, a pair of input terminals receiving the incoming signal and one of said terminals connected to the second and third flying brushes and to the third segment, a pair of batteries of equal potential connected in opposite polarity to the other input terminal and the opposite sides of said batteries connected respecfully, to the first and second segments, a pair of output terminals, one output terminal connected to the first flying brush and the other one connected to the second input terminal, a fourth relatively small segment mounted adjacent the second flying brush and engageable apropos "'7 therewitha pair of balancer tubes, a polar relay mounted in the plate circuit of said balanoer tubes, a first condenser connected between the grid of one of said balancer tubes and ground, the fourth segment connected to one side of said condenser, a three position switch movable be tween a pair of contacts and controlled by said polar relay, a phase control'motor connected to one of the contacts and engageable with the three position switch and supplying a first input to said differential, a frequency control motor connected tosaid three position switch and furnishing a shaft output to said frequency stand ard to adjust its output frequency, a coarse synchronizing circuit comprising fifth and sixth relatively small segments mounted closely adjacent one another and engageable with the third fiy ing brush, a second pair of balancing tubes, a second neutral relay connected. in the plate circuits of said balancing tubes, the fifth segment connected to the grid of the third balancing tube through a battery which has the negative side connected to the grid, a segment connected to the grid of the fourth balancing tube through a battery which has the positive side connected to the a second two position switch controlled by said second neutral relay and connected to said phase control and frequency control motors, and a third two position switch controlled by said second relay and in series with the first three position switch so as to disconnect it when the second relay is energized.

3. A synchronizing system for a teletype ceiver comprising, a synthetic start and stop pulse generator which receives the incoming signal, a fine synchronizing detector receiving the incoming signal, a coarse synchronizing detector receiving the incoming signal, a frequency stand ard, a master driving means controlled by said frequency standaro, a frequency adjusting motor connected to frequency standard receiving inputs from said coarse detector, and a phase correcting motor 'cceiving an input from said synchronizing means and adjusting the of the output shaft of said master drivingmeans.

4. A synchronizing system for a teletype receiver comprising, a pair of input terminals receiving the incoming signal thereon, first, second and third flying brushes, the second and third flying brushes connected to one of said input terminals, a drive shaft connected to said. first, second and third brushes to drive them in synchronization, a differential connected to said drive shaft, a-master driving motor supplying an input to said differential to drive said first, second and third brushes, a frequency standard supplying an input to said masterdrivemotor to control its speed of rotation, a frequency. adjusting motor connected to said frequency standard to adjust its frequency, a phase control motor supplying a shaft output to said differential to vary the phase of the master drive shaft, the second flying brush engageable with a small segment at a position corresponding to the change from stop to start pulses, a fine synchronizing control circuit connected to said small segment and to said phase control motors, a pair of small segments mounted adjacent the third flying brush and corresponding to positions, respectively, of the start and stop pulses, and a coarse synchronizing detector receiving inputs from saidpair of segments and suplying outputs to said frequency control motor.

5. A synchronizing system for a teletype receiver comprising, a synthetic start and stop generator which receives the incoming signal, a coarse synchronizing detector which receives the incoming signal, a fine synchronizing detector which receives the incoming signal, a frequency standard, a master driving means controlled by said frequency standard and supplying shaftinputs to said fine and coarse synchronizing detectors and the synthetic start and stop pulse generator, a frequency adjusting motor connected to frequency standard and receiving an input from said coarse detector, and a phase correcting motor receiving an input from said fine synchronizing dete tor and adjusting the phase of the output shaft of said driving means.

6. liieans for synchronizing a teletype receiver with an incoming signal comprising, coarse synchronizing means, fine synchronizing means, a synthetic start and stop pulse generator, the incomi g signal supplied to said fine'and coarse synchronizing means and the synthetic start and stop pulse generator, a master driving means supplying a shaft input to said fine and coarse synchronizing means and, said start and stop pulse generator, a frequency standard supplying control input to said driving means, the coarse synchronizing detector supplying an input to said frequency standard, and a phase controlling means supplying an input to said master driving means and r ceiving an input from said .fine synchronizing detector.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,487,632 Wendt Nov. 8, 1949 2,495,945 Schuler Jan. 31, 1950 2,534,337 Canfora Dec. 19, 1950 

